It’s Your Fault You Threw Away the Napkin!
So, here’s what went down. This young woman took out her retainer while eating. She placed the retainer on a napkin and left it there before the OP came around and cleaned the table up. Not knowing what was inside the napkin, the OP tossed it out like all the other pieces of garbage. The mom went berserk and demanded they look for the retainer in the garbage bin.
The good news is that the OP found the retainer. The bad news is that they were probably exposed to all sorts of bacteria and viruses you’d normally find in piles of garbage. Sorry you had to do that, OP.